The increased fuel efficiency makes electric propulsion systems particularly suitable when large $\Delta V$ increments are required, such as during orbital transfers around a central body. On the other hand, low thrust systems operate for a significant amount of mission time, producing long thrusting arcs that have to be designed through appropriate continuous optimization techniques. The corresponding optimal control problem is indeed strongly nonlinear and it is much harder to solve than conventional high-thrust trajectory optimization. In this work, a flexible approach for the optimization of low thrust trajectories is presented. The orbit transfer problem is addressed, introducing a two-stage technique to produce continuous spacecraft trajectories that satisfy initial and terminal conditions defined along two different orbits while minimizing the fuel consumption and/or time of flight (TOF).